In the past, Si-containing polybutadienes (called Si-polyoils hereinbelow) have gained increasing significance as adhesion promoters (tackifiers) in mixtures of elastomer and mineral fillers see DAS 2,635,601 and U.S. Pat. No. 4,183,844, the latter's disclosure being entirely incorporated by reference herein. These contain, in addition to an unsaturated polymer chain, solely reactive silyl groups of the formula --SiXYZ, wherein X is a hydrolyzable alkoxy group of 1-6 carbon atoms, preferably a methoxy or ethoxy group, while Y and Z, independently of each other, either are the same as X or are hydrogen, alkyl of 1-8 carbon atoms, cycloalkyl of 5-12 carbon atoms, or optionally substituted phenyl of 6-12 carbon atoms. Si-polyoils usually have an average molecular weight of 400-4,000.
The starting materials used in the production of such Si-polyoils are frequently chlorine-containing silanes. The resultant products then contain chlorosilyl groups, which can conventionally be converted into alkoxysilyl groups, for example by reaction with alcohols or trialkyl orthoformates. The most important processes for the preparation of Si-polyoils are briefly sketched below:
1. Silanes containing at least one Si-H-bond can be chemically added to polybutadiene oils. For example, trichlorosilane is used as the starting compound according to the process of DAS No. 2,314,543=U.S. Pat. No. 3,920,714, the latter's disclosure being entirely incorporated by reference herein. ##STR1##
2. By a Diels-Alder reaction, according to the process of DOS 3,003,893, corresponding to U.S. application Ser. No. 230,483 of Feb. 29, 1981, the latter's disclosures being entirely incorporated by reference herein, Si-polyoils which contain cyclohexyl rings can be produced from polybutadienes containing conjugated double bonds and from silanes containing vinyl residues, such as, for example, vinyltrichlorosilane. ##STR2##
3. Polybutadienes not containing a conjugated double bond react along the lines of an "ene" reaction with vinyltrichlorosilane. ##STR3## See also DOS's 3022989 and 3028839, corresponding to U.S. application Ser. No. 273,289 of June 15, 1981, the latter's disclosure being entirely incorporated by reference herein.
Also see commonly assigned, U.S. applications Ser. Nos. 396,217 and 396,218, both filed on July 8, 1982, whose disclosures are incorporated by reference herein.
4. Finally, use of metathesis opens up two further possibilities for forming Si-polyoils. A polymerization can be conducted according to the method of German Patent 2,157,405=U.S. Pat. Nos. 3,857,825; 3,920,715 and 3,929,850, the disclosures of the latter three U.S. patents being entirely incorporated by reference herein, using cycloolefins, such as, for example 1,5-cyclooctadiene or 1,5,9-cyclododecatriene, in conjunction with Si-containing, open-chain olefins acting as regulators: ##STR4## or a copolymerization can be conducted according to DAS 2,314,543=U.S. Pat. No. 3,920,714, the latter's disclosures being entirely incorporated by reference herein, using cycloolefins in conjunction with other cycloolefins having a reactive silyl group.
The effect of the Si-polyoils as adhesion promoters between mineral substances, on the one hand, and elastomers, on the other hand, seems to be due to the fact that the Si residue enters into an interaction with the mineral components, while the olefinic portion can be conventionally crosslinked with the elastomer by means of sulfur or peroxides. A broader range of application of the Si-polyoils has not been achievable heretofore on account of their poor preservability, especially in the presence of traces of water. If Si-polyoils are exposed to atmospheric humidity during storage, superficial gelling occurs after only a short period of time, with subsequent pellicle formation due to intermolecular crosslinking. It is presumed that the number of reactive alkoxysilyl groups decreases in correspondence with the equation ##STR5## With progressing reaction, insoluble components are formed which are no longer uniformly distributed in an elastomer mixture. The usefulness of the Si-polyols as adhesion promoters is thus considerably restricted.
In polymeric, silyl-group-containing haloalkanes prepared from vinyl chloride and vinyltrialkoxysilane, troublesome gelling occurs even during copolymerization. It is known from DOS 2,437,093, that in such cases, the shelf stability can be increased by adding certain epoxides to the reaction charge prior to or under certain circumstances, also during reaction. Incorporation of these epoxides, however, effected after cessation of reaction cannot prevent the aforedescribed, interfering gelling phenomena. The process of DOS 2,437,093 thus remains unsatisfactory under practical conditions.